The processing of corn to produce: (a) protein, fiber and fat-containing ingredients for the feed industry, (b) grits, meals, flours, starches and/or syrups for food manufactures, and (c) binders, film-formers, and adhesives for technical industries is done using either a wet or dry milling process. In the wet-milling process, corn kernels are steeped for 30 to 40 hours in a warm solution of water and sulfur dioxide. During steeping, the corn kernels absorb water (swell) and soften, thereby loosening the matrix that holds the protein, fiber, germ and starch components together. After steeping, the corn is coarsely ground to break the embryo (germ) loose from the other components. The ground corn is then pumped into hydrocyclones that spin the low-density corn germ out of the slurry. The germ is washed to remove excess starch, dried, and further processed with mechanical and/or solvent processes to extract corn oil. The heavy phase/slurry leaving the germ separators is ground more thoroughly in an impact or attrition mill to release the starch and protein from the fiber present in the kernel. The suspension of starch, protein and fiber is then pumped over screens that recover the fiber, but allow starch and protein to pass through. The fiber is washed to remove any residual starch or protein, combined with the defatted germ and concentrated steepwater, and dried to produce corn gluten feed. The starch and protein suspension is then pumped to separators where protein is removed due to its low density compared to starch. The starch is washed to remove the last traces of protein. The protein suspension is dewatered and dried producing a 60.0 percent protein product that the industry refers to as corn gluten meal. The clean starch may then be dried or further processed into sweeteners or fermentation chemicals. Corn wet-milling is a capital-intensive process, but the cost of producing starch for further processing is offset by the sale of the resulting co-products; corn oil, corn gluten feed, and corn gluten meal.
The first step of the dry-milling process entails tempering clean corn with water to 20.0 percent moisture. While moist, the outer bran layer or pericarp, the germ, and tip cap loosen their attachment to and are separated from the starchy endosperm. The majority of the corn endosperm, known as the “tailstock”, proceeds through a degerminator, is dried, cooled and sifted. A portion of the endosperm is isolated as large flaking grits. Further separation is accomplished using roller mills, sifters, gravity tables, and aspirators so that an infinite variety of smaller grits, meals, and flours can be produced. The bran and germ are passed through another part of the degerminator as the “throughstock” stream. This stream is dried, sieved, and aspirated to recover the bran. Further processing separates the germ from any remaining endosperm. The “throughstock” produces germ for crude corn oil production; hominy feed; bran products; standard meal; and prime grits, meals, and flours.
Some researchers have developed ways to combine the low cost and speed in which germ, fiber, and endosperm may be separated in corn dry-milling with the efficiency of starch and protein separation provided by corn wet-milling to create a “hybrid” process. For example, U.S. Pat. No. 4,181,748 discloses the dry milling of corn to provide fractions of endosperm, germ, fiber, and cleanings, and the wet milling of the endosperm fraction using two distinct steeping steps to provide a mill starch slurry. In this reference the mill starch slurry is separated into a starch-rich fraction and a protein-rich fraction, and the protein-rich fraction is combined with the germ, fiber, and cleanings fraction from the dry milling process and the offals from starch refining to provide a feed product.
In another reference disclosing the further processing of dehulled and degermed dry milled corn products, U.S. Pat. No. 4,517,022, corn endosperm is slurried with water containing alkali and sodium sulfite, and subjected to high intensity mixing for a period not to exceed four hours. A high quality starch is then recovered.
Due to its availability, relatively low cost, and high starch content, corn also is used as a raw material in the manufacture of fermentation chemicals. Ethanol is one such chemical, and is produced in large volume. Currently, ethanol is produced from corn mainly via two different processes—a wet mill process and a dry-grind process. The wet mill process follows the scheme described above with the resulting clean starch stream undergoing liquefaction, saccharification and fermentation. Ethanol is recovered by distillation and yeast is harvested and sold to feed manufacturers as a source of single cell protein. In the dry-grind process, raw corn is ground to a meal and mixed with water and enzymes. The corn slurry is cooked to gelatinize and liquefy the starch. The cooked slurry or mash is then cooled, a second enzyme is added to saccharify the liquefied starch (producing fermentable sugars), and yeast is added to ferment the sugars as they are processed to ethanol. The fermented mash is then distilled to recover the ethanol. Only starch is fermented to ethanol, the non-fermentable components of the corn (the oil, fiber, and protein) are carried through the process and emerge from distillation in slurry form. This slurry is centrifuged to separate the suspended or insoluble solids from the soluble solids, the insoluble solids being discharged from the centrifuge as a wet cake. The soluble solids are concentrated by evaporation, combined with the wet centrifuged solids, and dried together to produce distillers dried grains with solubles, or DDGS.
A derivation of the dry-grind ethanol process is disclosed in U.S. Pat. Nos. 4,407,955 and 4,448,881. Starch derived from a dry milled cereal grain (the starch in the form of corn endosperm) is hydrolyzed to provide a sterile aqueous fermentable sugar solution. Following an initial hydrolysis to liquefy the starch, substantially all of the water insoluble protein and oil components and a portion of the water-soluble components, e.g. sugars, lipids, proteins, and vitamins, are separately recovered from the hydrolyzate either before or after further hydrolysis of the liquefied starch to provide an aqueous solution of fermentable sugar. Unlike the traditional dry-grind ethanol process the insoluble, non-starch solids are removed prior to fermentation and do not contain yeast and yeast cell fragments, and the resulting minerals, vitamins, and unidentified growth factors contributed by the yeast to the DDGS.
Distillers dried grains with solubles (DDGS) contribute significantly to the economics of the dry-grind ethanol production process. Approximately 16.0 to 18.0 pounds of DDGS are produced from each bushel of corn processed. Its sale enables the ethanol producer to take a credit of $0.85 to $0.90 per bushel against his purchase price of corn. Distillers dried grains with solubles (DDGS) contains 3.5 times the protein (60.0 percent of which is by-pass protein in the rumen digestive system), 5.0 times the fiber (much of which has been made digestible for the rumen digestive system by the features of the process), and 7.0 times the fat of the starting corn. Approximately 85.0 percent of the DDGS produced is used as an ingredient in feeds for dairy cattle. Turkey, swine, and beef cattle represent expanding, but secondary markets for DDGS.
A significant amount of research has been conducted by animal nutritionists to demonstrate that DDGS produced by dry-grind ethanol production facilities may replace a portion of the corn, soybean meal, and calcium now used to formulate feeds for swine, poultry and beef cattle. The results of this research are that DDGS may be used, up to a certain level, but its selling price must stay in the range of $85 to $100 per ton to provide an incentive for its use. One of the limitations to the greater use of DDGS is its high non-starch carbohydrate content. Non-starch carbohydrates are the primary components of the cell wall, the hull, of cereal grains and are relatively resistant to breakdown by the digestive system of non-ruminants (swine, poultry, fish and pets). This prevents the nutrients entrapped within the cells of many grains and by-products of grain processing from being nutritionally available to the animal.
Enzymes are now being added to feeds to improve their digestibility and nutritional performance. U.S. Pat. Nos. 5,612,055 and 6,162,473 disclose methods to increase the efficiency with which monogastric animals utilize diets containing cereals and cereal by-products. The addition of hemicellulase, protease, and/or beta-glucanase enzymes to the rations increases the efficiency with which monogastric animals utilize the rations (the amount of feed consumed relative to the weight of the animal is reduced).
Other researchers have explored the prospect of further processing DDGS to increase its protein and decrease its fiber content. Wu and Stringfellow (Journal of Food Science 1982. Volume 47: 1155-1157) reported that pin milling and sieving may be used to isolate a high protein fraction from DDGS. Corn DDGS at 21.0 and 30.0 percent initial moisture protein, respectively, can be ground twice at 14,000 rpm and separated with a 50 mesh screen to obtain a fraction with 43.0 percent protein content in 41.0 percent yield.
There are no reports of a method that entails the dehulling and degerminating of corn to recover low fat, low fiber endosperm at the greatest yield possible (achieved by combining the large, medium and small grits, and the meal and flour streams produced during degermination of corn), and the use of enzymatic hydrolysis to solubilize and alcoholic fermentation to assimilate the starch and non-starch carbohydrates present in this corn endosperm in order to produce a highly digestible, high protein product (high protein distillers dried grains or high protein DDG). Additionally, there have been no reports of a method to produce a high protein DDG that is further characterized by its overall low fiber content (crude, acid detergent and neutral detergent fiber combined). Furthermore, there have been no reports of a method combining mechanical removal of corn fiber (bran) and enzymatic hydrolysis and alcoholic fermentation of non-starch carbohydrates to produce high protein DDG and the subsequent use of that high protein DDG as an ingredient in feeds for farm-raised ruminants and non-ruminants and in pet foods to improve the palatability and digestibility of animal feeds and/or pet foods, and aid in the management of the health and weight gain of the animal. It is an object of this invention to provide such a method and to also provide the composition produced by such method.